There is a hybrid work machine configured to operate a work unit or the like by driving a generator motor with an engine and driving a motor with power generated by the generator motor. For example, Patent Literature 1 discloses a technology in which a hydraulic pump and a generator motor are driven by an engine, and a battery is charged by generation action of the generator motor, and further an engine is assisted by driving the generator motor with battery power. Further, Patent Literature 1 discloses the technology in which output of the generator is restricted until an engine rotation speed reaches a setting speed at the time of accelerating the engine so as to assist acceleration by reducing an engine load.
Furthermore, Patent Literature 2 discloses a technology in which whether to cause a generator motor to execute engine torque assist action or not to execute engine torque assist action is determined. In the case of determining to cause the generator motor to execute the engine torque assist action, the generator motor is caused to execute the engine torque assist action, and in the case of determining not to cause the generator motor to execute the engine torque assist action, the generator motor is caused to execute generation action in accordance with a requested generation amount.